The present invention relates in general to semiconductor devices and their fabrication. More specifically, the present invention relates to improved fabrication methodologies and resulting structures for vertical field effect transistors (VTFETs) having improved gate length control based at least in part on incorporating relatively thin and uniformly deposited/etched spacers to define the gate length dimension.
Semiconductor devices are typically formed using active regions of a wafer. In an integrated circuit (IC) having a plurality of metal oxide semiconductor field effect transistors (MOSFETs), each MOSFET has a source and a drain that are formed in an active region of a semiconductor layer by implanting n-type or p-type impurities in the layer of semiconductor material. A conventional geometry for MOSTFETs is known as a planar device geometry in which the various parts of the MOSFET device are laid down as planes or layers.
One type of MOSFET is a non-planar FET known generally as a VTFET. VTFETs employ semiconductor fins and side-gates that can be contacted outside the active region, resulting in increased device density and some increased performance over lateral devices. In VTFETs the source to drain current flows in a direction that is perpendicular to a major surface of the substrate. For example, in a known VTFET configuration a major substrate surface is horizontal and a vertical fin extends upward from the substrate surface. The fin forms the channel region of the transistor. A source region and a drain region are situated in electrical contact with the top and bottom ends of the channel region, while a gate is disposed on one or more of the fin sidewalls. An important parameter in VTFET designs is the gate length (Lgate).